When you use nonpersistent disk mode, all changes that you make during a session are recorded in a file rather than to the disk itself.

This invisible, unlinked file is called the redo log (a similar file is used for undoable disks). Although inaccessible through the file system, this file is created in the same working directory as the disk file for the VM by default. It is discarded after the session.

Note that if a particular VM session is particularly long with many disk I/Os, the file may grow in size and consume noticeable disk space on your host operating system. For this reason, you can specify a different location for all redo logs, using the VM configuration editor.